In order to enable detailed inspection of the light pattern produced on the fluorescent screen of a cathode-ray display device, such as a cathode-ray tube or an X-ray image intensifier tube, it is often necessary to make a permanent recording of such pattern which can be stored for a subsegment relatively lengthy study. This is particularly true when the pattern is the trace of a transient phenomenon appearing on the face of a cathode-ray tube used in a cathode-ray oscilloscope. Conventional devices used to record such a trace are photographic cameras which are supported adjacent the face of a cathode-ray tube and which have provision for a viewing device for visually observing the trace as the camera is recording it on film.
Still another disadvantage with which the prior cathode-ray tube cameras are associated is the fact that they do not provide for quickly and simply setting for a precise magnification of the recorded image or for easily changing the magnification of the recorded image without refocusing the camera, i.e., to get film images of different sizes relative to the cathode-ray screen trace. For example, a ratio of 1.0 between the film image and the cathode-ray tube may be desired for a full size image on a 4" by 5" film or a ratio of 0.9 for an image of maximum size on a 72 mm by 96 mm film.
Since the relative size of the film image is varied by varying the distance of the lens from the film, various techniques have been set out. For example, a bellows type camera might be used but such camera has produced complications involved in providing necessary additional support structure for the camera lens as only a rigid camera body construction is acceptable in combination with a rigid camera-supporting clamp housing on a typical oscilloscope arrangement. Another type of prior art suggests the provision of a camera in modular form so that it may be quickly disassembled into its various components in order to enable the interchange of lenses having different optical characteristics such as focal length and maximum f-stop rating, and the interchange of lenses having different preset magnifications built into their lens mounts for changing the scale of the recorded image. While this type of prior art provides for a structure for varying the magnification of the lens while maintaining constant the respective distances from an object plane and an image plane which is simple and versatile, the solution is not fully satisfactory because of the necessity of keeping accessory lenses for the various focal lengths required which are quite expensive.
The most prevalent prior art solution is to provide so-called spacers or separate body sections for insertion to increase the distance between the camera lens and the film, there being one set of spacers of different dimensions to be inserted selectively for producing selected image ratios. This art is also not fully satisfactory because of the necessity of keeping a set of accessories available and because of the possibility of damaging, mislaying or losing one of the accessories and because of refocusing requirements.